In a first that should be noted in the presidential archives, the White House on Friday used the Twitter feed to announce to more than 726,000 followers that Obama is holding a press conference Wednesday night:

The blast — which went to the journalists subscribing to the feed as well — circumvented the past practice of leaking the news about the press conference to a particular news outlet (as the White House did this winter). It also happened nearly two hours before the press shop informed the non-tweeting correspondents who cover the administration.

Rather than wait until the news networks disseminated the information, Obama went right to the source.

elected is replaceable;Ak WILL progress! + side benefit=10 dys til less politically correct twitters fly frm my fingertps outside State site

Sen. John McCain last week sent out a press release boasting he’d hit 1 million Twitter followers (Tweeps, to some). He uses the feed to talk policy, promote his own television and radio appearances and on Thursday, to congratulate The Office’s Rainn Wilson for an Emmy nomination.

Also worth noting, the four candidates running for governor in Virginia and New Jersey in November all are on Twitter. (See Sarah Abruzzese’s story about the Virginia candidates’ tweets here.)